1. Field of the Invention
This invention relates in general to artificial lift devices and, in particular, to controlling an operation of an artificial lift device by monitoring waves resulting from an acoustic ping.
2. Description of the Prior Art
It is known in sonar and well logging technology to utilize an acoustic ping to estimate a distance to an object or a sonic velocity of a material. An acoustic ping is a pulse of sound, which is generated by a transmitter, is propagated as a wave through a medium, is typically reflected off an object or a change in propagation media, and then is collected by a receiver for analysis. An acoustic ping can also refer to a series of pulses. The sonic velocity of a material is the speed in which sound travels through the material (including sound having sonic, ultrasonic, or subsonic frequencies). The sonic velocity of a material can also be known as the velocity and as the ultrasonic velocity; it is affected by density and elasticity of the material. Sonic velocity is known to be a constant in a given material, and various concentrations of solutions can have different sonic velocities.
Various waves are well known in sonar and well logging technology. A P-wave is a wave in which particle motion is in the direction of source propagation. A P-wave is also called a compression wave, primary wave, pressure wave, or longitudinal wave. A S-wave, also called a shear wave or transverse wave, is a wave in which particle motion is perpendicular to the direction of propagation. In well logging technology, it is common to monitor the pressure “P” velocity, as well as shear “S” wave velocity, through a well formation to estimate the oil and water content. The T-wave, or tube wave, is the reflection from the top of the fluid or bottom of the well and is generally considered interference in well logging.
Ultrasonic flow meters are also known. An ultrasonic flow meter measures the velocity of a fluid (liquid or gas) in a pipe using acoustic sensors. One common type of ultrasonic flow meter is the transit-time flow meter, which works by measuring the “time of flight” difference between an acoustic ping sent in the flow direction and an acoustic ping sent opposite the flow direction. The time difference is a measure for the average velocity of the fluid along the path of the pings. By using the absolute transit time and the distance between the ultrasound transducers, the current speed of sound is easily found. Another type of ultrasonic flow meter measures the Doppler shift resulting in reflecting an acoustic ping off either small particles in the fluid, air bubbles in the fluid, or the flowing fluid's turbulence.
Today, downhole artificial lift devices typically use downhole pressure sensors to estimate a depth of fluid above an inlet of the device. Downhole artificial lift devices can include electrical submersible pump (ESP) assemblies, progressing cavity pump (PCP) assemblies, rod pumps, and downhole gas compressors. This prior art approach has numerous disadvantages. For example, pressure measurements can be unstable at the high temperatures of a well-bore environment. Also, in holes not drilled vertically, pressure measurements can provide imprecise estimates of the depth of fluid above a downhole artificial lift device. In addition, foam that accumulates on the well fluid surface provides another source of error.